Multipane glazing structures have been in use for some time as thermally insulating windows, in residential, commercial and industrial contexts. Examples of such structures may be found in U.S. Pat. Nos. 3,499,697, 3,523,847 and 3,630,809 to Edwards, 4,242,386 to Weinlich, 4,520,611 to Shingu et al., and 4,639,069 to Yatabe et al. While each of these patents relates to laminated glazing structures which provide better insulation performance than single-pane windows, increasing energy costs as well as demand for a superior product have given rise to a need for windows of even higher thermal insulation ability.
A number of different kinds of approaches have been taken to increase the thermal insulation performance of windows. Additional panes have been incorporated into a laminated structure, as disclosed in several of the above-cited patents; typically, incorporation of additional panes will increase the R-value of the structure from R-1 for a single-pane window to R-2 for a double laminate, to R-3 for a structure which includes 3 or more panes (with "R-values" defined according to the insulation resistance test set forth by the American Society for Testing and Materials in the Annual Book of ASTM Standards). Southwall Technologies Inc., the assignee of the present invention, has promoted such a triple-glazing structure which employs two glass panes containing an intermediate plastic film. Such products are described, for example, in U.S. Pat. No. 4,335,166 to Lizardo et al.
In multiplane structures two or more glazing panes are positioned in a spaced parallel relationship to one another by reason of spacers located at the periphery of the glazing panes. An effective spacer should have structural integrity and a substantial level of crush strength so as to allow a dimensionally stable window unit to be formed.
Spacers used heretofore have ranged from solid or open metal or plastic constructs to hollow metal, plastic, or composite tubes of circular, rectangular or irregular cross-sections, with continuous or discontinuous peripheries. Hollow spacers are often filled with desiccant to minimize interpane water content and condensation problems in the inner surface of the panes.
Examples of spacers in the art include U.S. Pat. Nos. 3,935,351 to Franz, 4,120,999 to Chenel et al., 4,431,691 to Greenlee, 4,468,905 to Cribben, 4,479,988 to Dawson and 4,536,424 to Laurent relate to spacers for use in multipane window units.
In this application's commonly assigned parent, U.S. patent application Ser. No. 389,231, filed 2 Aug. 1989, it is disclosed that a closed-cell polymer foam spacer can be employed to an advantage as a spacer in multipane windows and especially in high performance, gas-filled quadruple-pane glazing structures. References to spacers made from other types of foams include U.S. Pat. Nos. 4,563,843 to Grether et al. and 4,831,799 to Glover et al.
As higher and higher R values are demanded from multipane window units, there is an increasing need to minimize or at least reduce the conduction of heat through the edge spaces whenever possible. This invention addresses this need.
Despite the increasing complexity in the design of insulating window structures, total window R-values have not surpassed 4 or 5. While not wishing to be bound by theory, the inventors herein postulate several reasons for the limited insulating performance of prior art window structures: (1) thermal conductance across interpane spacers as discussed above present at the window edge; (2) thermal conductance within and across the edge sealant; and (3) the impracticality, due to considerations of window weight and thickness, of having a large number of panes in a single glazing structure.
The present invention addresses each of the aforementioned problems and thus provides a novel multipane window structure of exceptionally high thermal insulating performance.
In addition to insulating performance, the following characteristics are extremely desirable in a window structure and are provided by the present invention as well:
durability under extremes of temperature; PA1 resistance of internal metallized films to yellowing; PA1 resistance to condensation, even at very low temperatures; PA1 low ultraviolet transmission; and PA1 good acoustical performance, i.e., sound deadening within the multilaminate structure.